The U.S. says it will not recognize the outcome of Russian parliamentary elections planned for Crimea Sunday, the first since Russia annexed the Ukrainian peninsula in 2014.

"The United States does not recognize the legitimacy, and will not recognize the outcome, of the Russian Duma (lower house of parliament) elections planned for Russian-occupied Crimea on September 18th," State Department spokesman John Kirby said in a statement.

"The peninsula remains an integral part of Ukraine. Crimea-related sanctions against Russia will remain until Russia returns control of Crimea to Ukraine,” the statement said.

"We also continue to be deeply concerned about the humanitarian situation in Crimea, including the status of the ethnic Tatar community and widespread reports of missing persons and human rights abuses," Kirby said.

Ukrainian Foreign Minister Pavlo Klimkin said the elections are "completely illegitimate" and expressed concerned about the "extreme” number of Russian troops in Crimea.

Meanwhile, a group of unidentified anti-Russian protesters attacked Moscow's embassy in the Ukrainian capital Kyiv with fireworks in the early hours of Saturday.

Protesters take part in a rally against Russian plans to hold parliamentary elections in annexed Crimea, near the Russian embassy in Kyiv, Ukraine, Sept. 17, 2016.

The protesters were holding a banner reading: "Russian pigs, you are not welcome here. Fireworks today, Grads (cluster-fired rockets) tomorrow.”

They also chanted, "Freedom to prisoners of the Kremlin," and, "There will be no elections."

Russia annexed Crimea in March 2014, following a local referendum the U.N. General Assembly nearly unanimously called illegal.

Russian President Vladimir Putin has admitted his soldiers moved into the strategic Black Sea peninsula before the referendum took place, but has repeatedly denied backing the pro-Moscow insurgency in eastern Ukraine that has claimed nearly 10,000 lives since it began in April 2014.